Master of Science (M.Sc.)
Virginia Institute of Marine Science
Michael A Unger
Rachel E Sipler
Cultural eutrophication, the overproduction of phytoplankton biomass in response to increased nutrient inputs directly associated with human activities, is a major threat to the health of Chesapeake Bay. Strict regulations, which require a reduction in nutrient loading from all sources, have been a key component to restoration efforts. Water reclamation facilities (WRFs), which discharge effluent containing nitrogen (N) and other nutrients into receiving waters, have implemented upgrades in an effort to comply with regulations. These improvements have decreased the concentration of highly labile dissolved inorganic N (DIN), leaving behind significant concentrations of dissolved organic N (DON) whose bioavailability, and therefore its contribution to eutrophication, remains unclear. The concentration and composition of the N forms in effluent depend upon the characteristics of the influent entering the facility, the processes used to treat the wastewater, and the disinfection procedures employed prior to discharge. To investigate how these factors affect the composition of the effluent, samples were taken from four bench scale sequencing batch reactors designed to mimic commonly used treatment processes: nitrification only (NO), nitrogen removal (NR), biological nitrogen and phosphorus removal (BNPR), and biological nitrogen and phosphorus removal with additional chemical phosphorus removal (BNCPR). Effluent from each treatment process was also subjected to three disinfection procedures: no disinfection, ultraviolet radiation, and chlorination. To assess bioavailability, effluent from each of the treatment-disinfection combinations was added to natural water samples collected in the York River, VA. Results showed that total dissolved nitrogen (TDN) removal efficiencies of the treatments varied significantly from 12 to 98% and followed the trend NO < NR < BNPR < BNCPR. NO and NR produced effluent composed primarily of nitrate, while BNPR and BNCPR produced effluent composed primarily of DON. Bioassays showed that effluent from NO and NR stimulated phytoplankton growth, and that between 17 and 48% of effluent DON (EDON) was labile. Effluent from BNPR and BNCPR generally stunted or impeded phytoplankton growth and between 4 and 14% of EDON was labile. Overall, disinfection procedures had minor effects on effluent composition and bioavailability, indicating that the largest impacts on cultural eutrophication are made at the initial treatment level. This study provides results aimed at characterizing the composition of effluent resulting from both treatment and disinfection processes, eliminating influent as a variable. The data show that the discharge of NO and NR effluents would likely lead to eutrophication in both N and P limited receiving waters due to their high inorganic nutrient content and labile EDON. In contrast, the discharge of BNPR and BNCPR effluents, due to their low inorganic nutrient and relatively refractory DON concentrations, is less likely to contribute to eutrophication.
© The Author
Roberts, Quinn Nicole, "Composition and Bioavailability of Effluent Dissolved Organic Nitrogen" (2020). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1681950283.
Environmental Microbiology and Microbial Ecology Commons, Environmental Sciences Commons, Marine Biology Commons